Investigators said they believe the letter, written on Oct. 22, mailed the next day and delivered to her mother, Zenya Hernandez, on Nov. 6, was written by Hernandez.

"The reason we're announcing this today is that law enforcement had to take very possible step to verify its authenticity, and at this juncture, we believe it was written by Abby and sent to her mother," said Associate Attorney General Jane Young.

The FBI believes the North Conway teen is alive, but in "grave danger."

KIMBERLY BOOKMAN IS LIVE WHERE A AB BBY VANISHED TWO MONTHS GUY. WE ARE OUTSIDE A STORE WHERE YOU CAN SEE THEY HAVE A MISSING PERSONS SIGN OUT HERE TO REMIND PEOPLE. WE TALKED TO FOLKS IN THE AREA AND THEY SAY THEY ARE THRILLED TO HEAR THAT ABBY IS ALIVE. ABIGAIL HERNANDEZ'S MOM AND SISTER STAND WITH THE F.B.I. AND LAW ENFORCEMENT AS THEY DROP IN BOMBSHELL. A LETTER WRITTEN ON OCTOBER 22ND AND POST MARKED ON OCTOBER 23 WAS RECEIVED BY ZENNIA ON NOVEMBER 6. THE LETTER IS PURPORTED TO BE WRITTEN BY ABBY TO HER MOTHER. THIS CONTACT WAS MADE TWO WEEKS AFTER THE NORTH CONWAY TEEN VANISHED WALKING HOME FROM SCHOOL. WHEN WE RECEIVED THE LETTER I WILL TELL YOU IT WAS UNPRECEDENTED. WE HAVE NOT SEEN ANYTHING LIKE THAT IN RECENT TIME IN OTHER INVESTIGATIONS FROM THE EXISTENCES OF THE LETTER WAS KEPT PRIVATE SO INVESTIGATORS COULD VERIFY IT DID IN FACT COME FROM THE 15-YEAR-OLD. THEY WOULD NOT REVEAL WHERE IT WAS MAILED FROM OR ITS CONTENTS BUT SAY WHILE IT PROVIDES HOPE THEY ARE CONCERNED ABOUT HER WELL BEING. SOMEONE MAY NOW BE COERCING HER OR MANIPULATING HER. THE F.B.I. ADDED ONE IN EIGHT ENDANGERED RUNAWAYS ENDS UP BEING SEXUALLY EXPLOITED. ALONG WITH REVEALING THE LETTER AUTHORITIES SHOWED THESE PICTURES OF A NECK LACE AND POCKETBOOK THEY BELIEVE ABBY HAS WITH HER. WE WILL DO EVERYTHING WE CAN TO REUNITE HER WITH HER MOTHER. AND AUTHORITIES SAY THERE WAS ONLY ONE LETTER AND SO FAR NO ONE HAS HEARD FROM ABBY SINCE. THEY ARE ASKING THE PUBLIC TO KEEP AN EYE OUT IN THE COMMUNITY IF THEY SEE ANYONE WHO LOOKS OUT OF PLACE AND IF